This application claims the priority of Korean Utility Model Application No. 2004-12269 filed on May 1, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of Invention
The present invention relates to a keypad as a switch device for generating a signal in communication equipment, and more particularly, to an electroluminescent (EL) metal dome keypad configured in such a manner that an EL element is used as a light-emitting source and backlighting and switching functions are both included.
2. Description of the Prior Art
Generally, a keypad is a switch device for generating a signal, which is used for an electronic communication equipment such as a mobile phone or a remote control. The keypad has a separate light-emitting function that allows numeral- or character-printed keys to be identified and used at night or in dark places. The types of keypads having a light-emitting function will be discussed along evolved processes. Examples of such keypads include a LED type keypad, an EL sheet embedded keypad, an EL dome tape type keypad, an EL metal dome integrated keypad, and the like.
FIG. 1 is a sectional view of an LED type keypad. If any of protrusions 121 of the key top 120 are pressed, a relevant dome 150 is deformed and contacts with a fixed contact terminal 171 in a printed circuit board 170. Such a switching operation enables a power supply voltage from the printed circuit board 170 to be applied to a light emitting diode (LED) 160. The LED emits light and illuminates the key top 120.
However, in this LED type keypad, light emitted from the LED 160 is not uniformly delivered to the key top 120 positioned over the LED 160. It causes a problem that the visibility of numerals, characters, etc. printed on the keys, which outwardly protrude from the front case 110, is deteriorated and the uniformity of illumination is degraded. A use of a number of LEDs 160 can solve this problem, but it causes another problem of increased product cost and needs separate space for mounting the LEDs 160.
FIG. 2 is a sectional view of the EL sheet-embedded keypad disclosed in Korean Patent No. 10-384993, in which an EL is used as an emitting source and an EL sheet 230 is inserted into a key top 220. With this EL sheet-embedded keypad, the problem associated with the above LED type keypad may be solved. However, there is a need for an additional working process of inserting the EL sheet 230 into the key top 220. In addition, there arises a problem in that such a complex structure of the key top 220 increases failure rates and increases production costs.
FIG. 3 is a sectional view of the EL dome tape keypad disclosed in Korean Utility Model Registration No. 20-325934. An EL is used as a light-emitting source. An EL sheet 340 is laminated on a printed circuit board 360, and a top tape 330 is laminated on the EL sheet 340 to protect the EL sheet 340. With the EL dome tape keypad, the problem associated with the aforementioned EL sheet-embedded keypad can be solved by simplifying the working process and reducing reflective proportion.
However, there are problems in that stability of the EL dome sheet type keypad is reduced due to a unique noise generated in the EL sheet 340 itself and the switching function of domes 350 cannot be smoothly performed due to difficulty in managing deviations resulting from the top tape 330 with a thickness of about 75 μm and the EL sheet 340 with a thickness of about 200 μm.
In other words, electrical noise generated in the EL sheet 340, vibrations due to trembling of the sheet itself, or the like have influence on the domes 350, and thicknesses of the top tape 330 and the EL sheet 340 increase the operation load for bringing the domes 350 into contact with fixed contact terminals 361 of the printed circuit board 360, thus leading to poor click sense. Further, an irradiation function, electro static discharge (ESD), or the like may cause a serious problem in product performance.
FIG. 4 is a sectional view of an EL metal dome integrated keypad applied with a switch, which is disclosed in Japanese Patent Laid-Open Publication No. 2004-79338. An EL is used as a light-emitting source. A base tape 440 for holding domes 460 is laminated on a printed circuit board 470, and an EL sheet 430 is laminated on the base tape 440. At this time, the EL sheet 430 and the base tape 440 are attached to each other by double-sided adhesive tape 450, which has holes larger than the diameter of the domes 460. In this EL metal dome integrated keypad, the stability of products can be increased by minimizing influence from unique noise generated in the EL sheet 430 itself, and the switching operation load can be reduced and the click sense can be improved by relatively reducing the thickness between protrusions 421 of the key top 420 and the domes 460, thereby solving the problem associated with the aforementioned EL dome tape keypad.
Meanwhile, the working process of the aforementioned EL metal dome integrated keypad will be discussed. The top surface of the base tape 440 is attached to one side of the double-sided adhesive tape 450, and the EL sheet 430 is attached to the other side of the double-sided adhesive tape 450. Subsequently, the domes 460 are attached from the bottom face of the base tape 440, and the base tape 440 is then attached to the printed circuit board 470. However, the following problem may arise in the working process. In other words, the position of the base tape 440 where the domes 460 will be attached cannot be exactly recognized, whereby it would yield numerous difficulties in the working process and cause potential defects. Further, since there is no additional means capable of holding the attached domes 460, it is likely that the dome 460 will deviate during the working process. In this EL metal dome integrated keypad, outer surfaces of the domes 460 and fixed contact terminals 471 of the printed circuit board 470 are stained with the adhesive coated on the bottom surface of the base tape 440, and the adhesive is then increasingly soaked into the dome 460. Therefore, this may cause inferior contact between the domes 460 and the fixed contact terminals 471.